Abstract: An aqueous gel containing a crosslinking agent comprising an organozirconate chelate and a rate retarding agent which delays crosslinking of the gel or a rate accelerating agent which accelerates crosslinking of the gel. The retarding agent comprises a selected aldehyde or dialdehyde. The accelerating agent comprises a member selected from a group of polyamines. In the preferred embodiment, the crosslinking agent and crosslinking rate retarder or accelerator are injected simultaneously, yet independently, into an aqueous gel while introducing the gel into a subterranean formation sought to be fractured. The viscosity of the gel increases over a period of time which is controllable by altering the quantity of rate retarding agent or accelerating agent delivered in conjunction with a fixed concentration of crosslinking agent.

Abstract: A method of controlling crosslinking reaction rate in a water based polymer fracturing fluid that involves using a mixture of a crosslinker, in combination with a crosslinking rate accelerator or a crosslinking rate retarder at a ratio such that the crosslinking reaction rate is controlled. This decreases the shear effects upon the polymer fracturing fluid during pumping which affects downhole stability of the fluid and decreases pumping and frictional pressures. The ratio of rate accelerator or rate retarder to crosslinker for a desired crosslinking reaction time is dependent upon pH, surface temperature, polymer concentration, salt concentrations, fluid loss additives, surfactant types and concentrations, mutual solvents and alcohol. The preferred polymer fracturing fluid is a high pH aqueous salt solution including a hydroxypropyl guar polymer. The preferred crosslinkers are transition metal chelates. The preferred crosslinking rate accelerators are polyamines.